Pre-vaporizing and pre-mixing burner for liquid fuels

ABSTRACT

The invention concerns a pre-vaporizing and pre-mixing burner for liquid fuels which has a fuel feed line ( 56 ), a pump which pressurizes the fuel in the feed line, a mixing region ( 123 ) and a fuel valve ( 119 ) which opens out into the mixing region and by means of which the fuel is atomized and fed to the air for combustion ( 127 ). According to the invention, the fuel is vaporized in an optimum manner in that the fuel valve opens automatically as from a given fuel pressure, and a heating device ( 128 ) is associated with the fuel valve.

FIELD OF THE INVENTION

The present invention relates to a method for providing a combustiblemixture of a liquid fuel and combustion air, as well as a prevaporizingand premixing burner for liquid fuels, having one or several fuelheaters for heating the liquid fuel prior to combustion.

BACKGROUND OF THE INVENTION

In the field of household and small consumers (HuK) it is known to burnfuel oil EL for heating purposes or for purposes of thermal processtechnology in a pressure atomizer burner. The liquid fuel oil EL isconverted under high pressure (500 to 2000 kPA) into a fog of dropletsby means of an atomizer nozzle and is simultaneously mixed with thesupplied combustion air. A method exists in addition, wherein fuel oilEL is atomized by means of compressed air. Further than that there arevaporization burner devices, wherein the liquid fuel is vaporized on thesurface of a heated body which is surrounded by combustion air.

The following problems are connected with the present-day burners: inconventional oil burners, the liquid fuel oil EL is converted into a fogof droplets by means of an atomizer nozzle and simultaneously mixed withthe supplied combustion air. The processes, such as atomizing, mixing,vaporizing and gasification of the fuel, as well as the combustion ofthe gasified fuel, occur unregulated side-by-side and in an interactingmanner. The individual oil droplets are surrounded by a flame envelope.The high temperatures in the vicinity of the drops, together with thesimultaneously occurring lack of air, trigger cracking processes, bywhich soot is formed.

Present-day blue flame burners avoid the generation of soot in that theyvaporize the fuel at the flame root prior to combustion. Here hot fluegases returned from the flame zone here vaporize the oil spray emergingfrom a swirl nozzle. The water content of the returned flue gasesprevents the formation of long-chain hydrocarbons, which can only beburned along with the generation of soot. The method of recirculatingthe exhaust gases lowers the nitrous oxide emissions in addition to thesoot emissions. In order to convey a sufficiently large amount of hotflue gas into the flame root, a correspondingly large induction effectof the fuel/air jet within the mixture preparation is required. Theinduced mass flow is affected for one by the velocity of the emergingmixture flow and also by the cross section of the open jet. Bothparameters can only be varied within certain limits. A high outletvelocity leads to loud flow noises, an increased blower output and largeburner dimensions. An increase in the outlet cross section, togetherwith a reduction in velocity, leads to ignition conditions already beingcreated in the vaporization area, so that the intended fuelvaporization, which is uncoupled from the combustion reaction, does notoccur. Moreover, the pulse exchange between the fuel and the combustionair is reduced, by which the mixture is also negatively affected. Inaddition, a high outlet velocity at the twist generator prevents a flameformation in the near range of the mixing device and thereby leads to areduced thermal stress of these components. It follows from this that inconnection with present-day mixture preparation methods for oil burnersa reduction of the noxious matter emissions is always connected with anincrease in the velocity of the combustion air, and therefore leads toincreases in noise emissions and the required blower output.

In a burner system having a firing equipment output of 15 kW, areduction of the fuel oil flow rate is not possible with conventionaloil pressure atomizer nozzles. For reducing the throughput, the nozzlecross section cannot be further reduced for reasons of dependability.The pump pressure can also not be arbitrarily reduced, because theatomizing quality is clearly reduced.

Conventional oil burners are heterogeneous systems, i.e. the dispersedphase fuel oil EL and the dispersion medium air exist as discrete phasesside-by-side and are separated by a phase boundary. The roughlydispersed fuel distribution caused by atomizing does not make itpossible to mix the fuel without prior vaporization in front of theflame, because the individual fuel droplets settle under the effects ofgravity and are deposited on the mixing chamber walls. For this reason apremixing surface burner device, such as can be used in the field of gascombustion, is not possible.

Modem gas burner devices show that a reduction of the nitrous oxideemissions is most effectively achieved by means of a premixing burnersystem.

A gasification device for fuel oil and kerosene is known from Germanpatent DE-C2-24 56 526, and an oil heating device from German publishedapplication DE-OS 14 01 756, wherein the fuel is heated prior toatomizing. Although heating the fuel leads to improved and fineratomizing, problems occur because of cracking product depositions, suchas clogging of the lines, etc.

SUMMARY OF THE INVENTION

The above mentioned problems are solved by the present invention by theprovision of a method wherein: the liquid fuel is put under pressure ina heating phase with the fuel valve closed; the fuel under pressure andin liquid form is heated; following the heating phase the fuel valve isopened and the heated liquid fuel under pressure is atomized andvaporized through a nozzle; the vaporized fuel is mixed with combustionair, where at least a part of the vaporized fuel is condensed, so that acolloid-dispersed and/or a molecular-dispersed fuel-air mixture iscreated; the fuel valve is closed to terminate combustion; and, with thefuel valve closed, the heated and liquid fuel is cooled;

The advantages which can be achieved by means of the present inventionconsist in particular in that, with the method on which the presentinvention is based, a colloid-dispersed or molecular-dispersed fueldistribution occurs, depending on the degree of air preheating. A mixedform of both distribution types is also conceivable. Because of thestability of the colloid-dispersed fuel distribution, it is possible tomix the reactants ahead of the flame without the fuel droplets beingdeposited on the mixing chamber walls. Here, the mixing of the reactantsis possible completely spatially decoupled from the combustion reaction,and not, as with conventional emission-reducing oil burners (so-calledblue flame burners), only inside a very small gasification zone ahead ofthe flame, which is in direct convective heat exchange with the flamevia the flue gas recirculation. Because the mixture of fuel andcombustion air is now no longer limited to the gasification zone aheadof the flame, the premix burner devices known from gas burnertechnology, which make possible a very intensive mixing of thereactants, can now also be employed for liquid fuels. The knownadvantages of this burner technology are therefore also now usable forliquid fuels. Among these are:

(a) low emissions (soot, nitrous oxide, carbon monoxide) when using asurface combustion system;

(b) low noise emissions;

(c) small blower output required;

(d) a combustion air blower system can possibly completely omitted(atmospheric mixture formation);

compact heat generator construction because of the direct coupling ofthe heat exchanger on the heating cycle side to the reaction zone, whichcan be spatially exactly determined.

The core of the prevaporizing, premixing combustion technique isconstituted by the heating of the liquid fuel oil under pressure.Vaporization of the fuel oil only takes place at the nozzle outlet incontrast to conventional vaporization burner devices, wherein the oilimpinges with almost no pressure on a hot surface, which results in thedeposition of low-volatile fuel oil components. Maintaining the abovementioned pressure conditions in the operational phases, in which heatedfuel oil is in the hydraulic system of the burner, prevents thesedeposits. Both during the heating phase and during the cooling phase,the oil lines from the pump to the heated fuel valve are pressuresealed, or the pressure in the system is maintained by means of an oilpump or of a compensation vessel (for example metal bellows).

A fuel valve with “atomizing characteristics” is used in the system inaccordance with the present invention, which unblocks the nozzle openingstarting at a defined pressure. The oil vaporization triggered by thepressure reduction at the valve outlet causes an extreme increase involume, and therefore a considerable reduction of throughput incomparison with the operation of the fuel valve with fuel oil which wasnot preheated. When using a swirl nozzle, a reduction of the throughputis caused by the reduction in viscosity connected with preheating thefuel. The air core within the nozzle opening increases with increasingfuel temperature and the fuel throughput decreases. The extremepreheating makes it possible to design the nozzle opening considerablylarger, in particular with small throughputs, than would be possiblewith conventional pressure atomizer systems. Because of employing thetwist principle in a return flow nozzle with an integrated needle valve,the required output of the firing equipment can be further reduced.

In a further development of the present invention it is provided thatthe heating device is constituted by at least one electric heating rod,heating element or heating cartridge. The heating device is designed insuch a way that at maximum throughput the fuel is heated to the desiredtemperature. It is advantageous to provide the fuel valve additionallywith a temperature sensor, for example a thermal element or the like, sothat its temperature can be detected for regulating the heating outputof the heating device.

A particularly simple exemplary embodiment provides that the heatingdevice is placed into the fuel valve. In this case the individualheating cartridges or the like can be inserted into bores, for example.However, it is also conceivable that the heating device can be installedon the fuel valve, for example flanged to it, so that there is a directcontact between the heating device and the fuel valve.

With one exemplary embodiment, the fuel valve is embodied as a simplexnozzle with a closing piston. In this case the closing piston can belocated outside or inside of the fuel valve.

A further development provides that the fuel valve has a return flowopening and can be combined with a return flow line. A return flowsystem is created in this way and the fuel valve is used as the returnflow nozzle.

When the hydraulic system is laid out as a return flow system, directelectric heating of the valve, or respectively of the valve body, is notnecessary. It is sufficient to heat the fuel by means of an electricallyheated fuel heater which is remote from the fuel valve and is arrangedupstream of the fuel valve, viewed in the flow direction. Transferringthe fuel by pumping at a small pressure difference between the forwardflow and return flow pressure prior to opening the valve causes heatingof the fuel volume inside the valve. In this way the emergence ofinsufficiently heated fuel immediately following the opening of the fuelvalve is prevented.

The return flow nozzle can a for example a have an integrated needlevalve, which pressure-seals the nozzle opening during the heating andcooling phase. The movement of the valve tappet is made possible bymeans of the pressure difference between the forward and return flowpressure. Transferring the fuel oil by pumping at a small pressuredifference between the forward flow and return flow pressure prior toopening the valve prevents the emergence of insufficiently heated fueloil. For cooling the hot returned oil mass flow it is possible toadditionally provide an oil cooler, which heats the combustion air,upstream of the pump inlet. Depending on the degree of air preheating,the proportion of the gaseous fuel in the fuel/air mixture increases.The pulse exchange between the combustion air and the fuel, whichaffects the quality of the mixture, also increases with increasing airtemperature.

A further development provides that an adjustable flow resistor forpressure regulation, as well as an adjustable check valve, are providedin the return flow line.

With a return flow line which is merely used as a leakage line, nospecial measures for cooling the very small oil mass flow are necessary.For example, with a coaxial combination of the oil feed line and the oilreturn line, the cooling action of the fed-in oil mass flow issufficient. Finally, embodiments are known, with which a return flowline is not required.

A burner with a fuel valve terminating into free space immediately afterthe valve tappet has the advantage that, depending on the degree of airpreheating, a colloid-dispersed or molecular-dispersed dispersed fueldistribution occurs. Because of the stability of the colloid-disperse orrespectively the molecular-dispersed distributed fuel it is possible tomix the reactants already ahead of the flame in an area of large volumewithout the fuel droplets being deposited on the mixing chamber walls.Therefore, mixing of the reactants is possible completely spatiallydecoupled from the combustion reaction, and not, as with conventionalemission-reducing oil burners (so-called blue flame burners), onlyinside a very small gasification zone ahead of the flame, which is indirect convective heat exchange with the flame via the flue gasrecirculation. The low temperature of the quasi-homogeneous mixture ofthe burner in accordance with the present invention permits intensivemixing in a mixing zone of large volume without the danger ofspontaneous ignition. Now the mixing of fuel and combustion air is nolonger limited to the gasification zone ahead of the flame. By employinga return flow nozzle in connection with extreme preheating of the fuelunder pressure in particular, a small required firing equipment outputcan be achieved with operational dependability. Moreover, a largeadvantage is achieved in that deposits of cracking products areprevented, since the fuel vaporization takes place in the freeatmosphere and not, as in film vaporization burners, at a hot surface inthe presence of oxygen.

The heating zone is located in the direct vicinity of the reaction body,but is spaced apart from it. With another exemplary embodiment, theheating zone is connected directly with the reaction body. By means ofthis embodiment the fuel is heated during its passage past the heatingzone by the reaction body which, as a rule, is red hot during operation.Therefore separate heating devices are not required during operation. Inthis case heating can be accomplished by means of radiated energy, bymeans of convection or by direct contact by means of heat conduction.

With a particularly preferred exemplary embodiment the heating zone isdesigned as a ring conduit. In this way a comparatively large surfacefor the inflowing fuel is created, so that it can be rapidly heated, forexample by radiation. With a sleeve-like reaction body enclosing thering conduit in particular, a very large surface for heating isavailable.

With another embodiment it is provided that the heating zone is designedas a spiral tube. The fuel to be heated is conducted through this spiraltube, wherein the reaction body directly radiates against the spiraltube.

In the preheating phase prior to the start of the burner, the fuel isheated in that an electric heating cartridge is provided, which isconnected with the heating zone. In particular, the heating zone restsdirectly against the heating cartridge, so that the heat from theheating cartridge is transferred by heat conduction to the heating zoneand from there to the fuel. In this case the heating cartridge can bedesigned as a heating rod or a heating spiral.

In a preferred embodiment, sections of the heating cartridge are inconnection with the area through which the fuel-air mixture isconducted, wherein a flashback arrester is provided in the directiontoward the mixture preparation. In this exemplary embodiment the heatingcartridge is additionally used as an ignition device, wherein thefuel-air mixture is ignited on the casing of the heating element, whichas a rule is red hot. Separate ignition devices are thereforesuperfluous.

Further advantages, characteristics and details ensue from the claims aswell as from the following description, in which several preferredexemplary embodiments and variations are described in detail, makingreference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: is a schematic representation of a prevaporizing, premixingburner for liquid fuel according to the present invention;

FIG. 2: a shows an arrangement for the regulation of fuel feeding;

FIG. 3: is a first exemplary embodiment of a fuel valve with a closingpiston according to the present invention;

FIG. 4: a fuel valve with a closing piston designed in the way of asimplex nozzle;

FIGS. 5 to 7: are longitudinal sectional views of embodiments of theburner in accordance with the present invention; and

FIG. 6a: is a cross section of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fuel lines 113, the air-conducting components 114, the components115 conducting the fuel/air mixture, the components 116 conducting theflue gas and the water lines 117 of the heating circuit 144 areschematically represented in FIG. 1.

The burner in accordance with FIG. 1 comprises the functional units 118for air preparation, fuel preparation, 121 for air regulation, 122 forfuel regulation, mixing zone 123 and reaction zone 124.

The air preparation unit 118 consists of a heat exchanger 125 forpreheating air, which removes heat from the return flow of fuel 126 andtransmits it to the supplied combustion air 127.

The fuel preparation unit 119 consists of an electrically heated fuelheater 128, the heat exchanger 125 in the return flow line 126, which isconnected with the air preparation unit 118, and a heat exchanger 129,which transfers a portion of the heat being released during thecombustion reaction to the fuel preparation unit 119, and a return flownozzle 130 with an integrated needle valve.

The air regulation unit 121 consists of a blower 131 and an air throttle132, which can be actuated electro-mechanically or mechanically, bymeans of which an automatic adaptation of the conveyed air mass flow tothe actual air requirements of the firing equipment is possible.

When the burner is started, the burner control switches the burner motoron, which is coupled with the oil pump 62 (FIG. 2) and the blower 131.The check valves 53, 54 and 55 are initially closed. Thereafter, theelectro-mechanically actuable check valve 53 in the forward flow line 56and the electro-mechanically actuable check valve 55 in the side branch58 of the return flow line 57 are opened. Simultaneously the burnercontrol switches on the electrically operated heating element 133 in thefuel heater 128. In this operational phase, the oil pump 62 conveys thefuel through the fuel preparation unit 119 and the heat exchanger 125coupled to the air preparation unit 118. Because of the low pressuredifference between the measuring points 33 for the forward flow pressureand 134 for the return flow pressure 134, the needle valve in the returnflow nozzle 130 remains closed. This pressure difference can be variablyset by the mechanically operated pressure regulating valves 60 and 59.Here, the minimum pressure in this system corresponds to the pressurevalue which can be detected at the measuring point 134 for the returnflow pressure. Thus, an overpressure in comparison with atmosphericpressure prevails in all components through which the heated fuel flows.By means of this it is assured that no low-boiling fuel components arevaporized during the heating of the fuel and the remaining high-boilingfuel components do not form deposits in the hydraulic system. Moreover,the transfer of fuel by pumping prevents the premature emergence ofinsufficiently preheated fuel from the return flow nozzle 130.

By opening the electro-mechanically actuable check valve 54, the returnflow pressure drops in the swirl chamber of the return flow valve 130when the required oil temperature has been reached, and the needle valveunblocks the nozzle bore. Because of this, the fuel in the mixing zone123 is atomized and forms a combustible mixture with the fed-incombustion air 127, which burns in the reaction zone 124. Either aconventional high voltage ignition system or an electrically heatedignition element is provided for igniting the mixture. Anotherpossibility lies in using the high surface temperature of theelectrically heated fuel heater 128 for igniting the mixture.

The return flow nozzle 130 is designed as a swirl nozzle, the same as ina conventional pressure atomizer burner. The throughput is reduced withincreasing fuel temperatures. Moreover, the employment of a return flownozzle 130 has the advantage that, at constant forward flow pressure,the ratio of fuel conveyed back and the amount of atomized fuel can bechanged over a large range 1:10 by throttling the return flow pressure.

Preheating the fuel and the use of a return flow nozzle make it possibleto select the nozzle cross section considerably larger at the same oilthroughput than is possible with conventional pressure atomizer burners.A reduced clogging tendency of the nozzle opening and increasedoperational dependability of the system are the result.

With this method, the heated fuel, which is under pressure, is atomizedin the dispersion agent air. A portion of the vaporized molecules iscondensed into a colloid-dispersed system, the remaining portion ismaintained as a stable gas and forms a homogeneous mixing system, thesame as in a gas burner. The proportion of colloid-dispersed oildroplets and homogeneously mixed molecules is a function of the fuelcomposition, which is influenced by temperature- and pressure-dependentchemical reactions (for example cracking reactions in connection withthe fuel oil EL as fuel), and the degree of air preheating.

The colloid-dispersed distributed fuel in this system is aggregated intodroplets of such length that they are separated by a phase border fromthe dispersion agent, the air. On the other hand, however, the particlesare so small that in their behavior they correspond to a large degree todissolved molecules.

From this, the following advantages over a roughly dispersed fuel oildistribution of conventional pressure atomizer systems result: (a) thecolloid-dispersed oil droplets are distributed in the combustion airthrough Brownian movements until their concentration has reached thesame value at all locations of the system; (b) excellent constancy ofthe colloid-dispersed fuel; (c) the gaseous portion of the fuel forms acombustible mixture with the combustion air immediately following mixingby molecular transport. The laws of spray combustion apply to thecolloid-dispersed portion of the fuel, the same as with conventional oilpressure atomizer burners. The accelerated heating and vaporization ofthe drops because of the small drop diameters, and the chronologicallyadvanced combustion and the temperature increase connected therewith ofthe portion of the fuel already in the gas phase make it possible tospeak of a “quasi-homogeneous combustion systems , in spite of theportion of the fuel which is in the liquid phase.

The electrical heating element 133 is switched off during the operatingphase of the burner. The energy required for heating the fuel is takenout of the reaction zone 124. The heat exchanger 129 in the reactionzone and the fuel heater 128 are designed as a structural unit.

For turning off the burner, the burner control initially closes thecheck valve 54 in the return flow line 57 and the check valve 55 in theside branch 58 of the return flow line 57. Because of this the pressuredifference between the forward and return flows at the measuring points33 and 134 is reduced and the needle valve in the return flow nozzle 130is closed. The combustion reaction is interrupted by this. The highpressure in the fuel preparation unit 119 prevents the vaporization ofthe still hot fuel after the burner has been shut off. At the end, theburner control closes the electro-magnetic check valve 53 in the forwardflow line 56 and turns off the burner motor.

A first exemplary embodiment of a burner valve, identified as a whole by201, is represented in FIG. 3. This burner valve 201 has a housing 202with a valve nozzle bore 203, in which a feed line (not represented)terminates through an opening 204. Optimally the fuel valve 201 can beprovided with an additional opening 205, which also terminates in thevalve nozzle bore 203. A return flow line (not represented) can beconnected to this additional opening 205, so that the fuel valve 201 canbe used in a purely forward flow system as well as in a return flowsystem. When used with a forward flow system, the opening 205 is closedby a plug.

A valve nozzle 206, into which a valve tappet 207 has been inserted, isscrewed into the valve nozzle bore 203. This valve tappet 207 ismaintained in the closed position by means of a closing spring 208. Ifthe pressure in the valve nozzle bore 203 is increased past a definedvalue, the valve tappet 201 is pushed and the valve nozzle 206automatically opens.

It can moreover be seen in FIG. 3 that heating cartridges 209 have beeninserted into appropriate bores or other recesses of the housing 202. Ifthe housing 202 is heated by means of these heating cartridges 209,which are electrically operated, the fuel present in the valve nozzlebore 203 is also heated. In this way the valve nozzle bore 203 is usedas a preheating chamber 210. The fuel emerging from the valve nozzle 206is preheated, from which the above mentioned advantages ensue.

FIG. 4 shows a second exemplary embodiment of a fuel valve, identifiedas a whole by 211, which has a slightly altered construction. Thepreheating chamber 210 terminates in a simplex nozzle 212, which isclosed by a valve tappet 213. Here, too, the valve disk 214 is liftedoff the opening of the simplex nozzle 212 when the fuel in thepreheating chamber 210 has reached a defined pressure. Since thecharacteristics of a simplex nozzle are known, i.e. the reverselyproportionate connection between throughput and temperature of the fuel,this will not be further discussed here. It should be noted that theseat 215 of the valve tappet 213 has been represented in FIG. 4 merelyby way of example. Other constructions are conceivable and should alsobe covered by the present invention.

However, it is important that the fuel valves 201 and 211 are providedwith a heating device 216 constituted by heating cartridges 209, whereinthe heating cartridges 209 have been inserted into appropriate openingsin the exemplary embodiments. It is, however, also conceivable that theheating device 216 is interlockingly mounted on the fuel valves 201 and211. The housing 202 of the fuel valve 201, or respectively 211, isheated by means of the heating cartridges 209, and the fuel in thepreheating chamber 210 is heated via this housing 202. When a definedtemperature has been reached, or when the pressure of the fuel in thepreheating chamber 210 has reached a defined value, the valve tappet207, or respectively 213, is lifted and fuel can emerge from the fuelvalve 201, or respectively 211. The fuel, which is under pressure andheated, is nebulized in the course of expansion and can be optimallymixed with the possibly preheated combustion air.

A burner, identified as a whole by 301, is represented in FIG. 5, whichhas the construction described in what follows. A heat exchanger element303, in which the fuel is preheated, is located inside a dynamicallybalanced reaction body 302. It is fed through a supply line 304 to theheat exchanger element 303 and reaches a ring conduit 305 constituted bytwo concentric sleeves 306 and 307. The fuel is introduced into the ringconduit 305 through a connecting line 308, or respectively it is removedfrom the ring conduit 305 through a line 309. The line 309 terminates ina return flow nozzle 310, which is opened, starting at a definedpressure prevailing in the line 309 and atomizes the fuel into an innermixing chamber 311. Air conduits 312 furthermore terminate in thismixing chamber, through which combustion air is supplied. Thiscombustion air flows through the heat exchanger element 303 via a line313 as well as a ring conduit 314.

With the return flow nozzle 310 closed or opened, the fuel suppliedthrough the line 309 is returned into the tank through a return flowline 315. This return flow line 315 is located near the line 313, sothat the fuel in the return flow line 315 is cooled by means of the airflowing through the line 313, or respectively the air is heated by thisfuel. With large amounts of fuel conveyed back, a separate oil cooler isprovided, through which either the supplied combustion air or the oilmass flow, or both, flow.

The heat exchanger element 303 has a circumferential groove 316, intowhich a heating element 317 in the form of a heating spiral 318 has beeninserted. In the starting phase, this heating spiral 318 preheats theinner sleeve 306, and by the latter the fuel in the ring conduit 305.The fuel in the ring conduit 305 is under pressure here. The innersleeve 306 is pressed on the heating spiral 318 and welded on its frontfaces, so that the heating spiral 318 is fixed in place and protected.The heating spiral 318 can be additionally provided with a thermalelement (not shown).

The return flow nozzle 310 is located in a union nut 319, so that it canbe rapidly removed when needed, for example for repair or maintenancepurposes. The valve tappet 320, which is prestressed by a compressionspring 321, can be seen at the rear of the nozzle 310. The fuel valvecan also contain the spring as a structural unit.

The inner mixing chamber housing 322, around which the outer mixingchamber housing 323 is wrapped, has been placed on the union nut 319.Thus, there is a further mixing chamber 324 between the inner and outermixing chamber housing, which is used for further homogenizing thefuel-air mixture. The mixture is supplied from this outer mixing chamber324 to the reaction body 302 and flows through the latter radiallytoward the outside. After ignition, the mixture burns outside of thereaction body 302, so that the reaction body 302 is red hot duringoperation. The heat radiated by the reaction body 302 is radiallytransmitted toward the interior as well as toward the fuel-air mixturelocated between the reaction body 302 and the heat exchanger element 303and to the outer sleeve 307, so that the mixture and the fuel in thering conduit 305 are heated. The heating element 317, which is suppliedwith energy via the electric conductors 325, is switched off duringoperation, or respectively is operated in cycles, for example by meansof a regulator, for maintaining a defined temperature.

Flame monitoring at the exterior of the reaction body 302 takes place bymeans of a flicker detector 326 facing the inside of the fire chamber orthe premixing area and looking from below through the reaction body 302.Also possible is flame monitoring by means of an ionization electrodearranged above the reaction body or projecting inside it.

The embodiment of a burner represented in FIG. 5 has the considerableadvantage that the fuel is heated within a very short time, inparticular in the starting phase, because of the short distance of theoil film in the ring conduit 305 from the radiation source constitutedby the reaction body 302. In this case the heat flows radially from theinside to the oil film. During burner operation the output of radiatedheat from the reaction body heats up the outer sleeve of the ringconduit. The latter transfers the heat to the oil film. During thestartup of the burner, the oil film is correspondingly heated radiallyfrom the inside, during burner operation heating is provided by the heatoutput (radiation, conduction) of the reaction body.

The ring conduit 305 moreover offers a large heat exchanging surface.The dynamically balanced reaction body 302 can alternatively also beembodied as a flat bottom wherein, in place of the ring conduit 305, aheat exchanger for heating the fuel must also be provided directlyunderneath this flat body.

In the exemplary embodiment of FIG. 6, the heat exchanger element 303directly contacts the reaction body 302, so that the fuel in theconnecting line 308 is heated by heat conduction. The heating element317 for heating the fuel in the starting phase is designed as a heatingrod 327, which is inserted into a corresponding bore 328 (see FIG. 6a)of the heat exchanger element 303. This bore 328 is broken opensegment-like over a part of its length, so that the heating rod 327 isopenly accessible in this area 329. This area 329 is in connection viaan opening 330 and a connecting line 331 with a chamber 332, whichitself is connected via the ring conduit 333 with the outer mixingchamber 324. In this way the fuel-air mixture, which can enter theopening 330 via the connecting line 331, can be ignited by the red hotheating rod 327 at the end of the starting phase, so that the flame canpenetrate through the reaction body 302, by means of which the burner301 is started. A flashback of the flame through the opening 330 intothe chamber 332 is achieved by means of the comparatively small crosssection of the connecting line 331 and its length, so that a dependableflashback arresting device is created. The great velocity of thefuel-air mixture and the small distance between the surfaces and therelatively great length of the surfaces (extinguishing distance) of theconnecting line 331 prevent the ignition of the mixture in the chamber332.

In the exemplary embodiment in FIG. 7, the heat exchanger element 303 iswrapped in a spiral tube 333, in which the fuel is conducted. Thisspiral tube 333 is connected both to the connecting line 308 and theline 309, wherein the flow through the spiral tube 333 is also acounterflow. This spiral tube 333 is irradiated by the reaction body322, so that the fuel flowing in it is heated.

What is claimed is:
 1. A prevaporizing and premixing burner for liquidfuels, comprising: at least one fuel heater for heating the liquid fuel;means for increasing the pressure of the liquid fuel; a nozzle foratomizing and vaporizing the fuel and for mixing the fuel withcombustion air, wherein at least a portion of the vaporized fuelcondenses, creating thereby one of: a colloid-dispersed fuel-airmixture, a molecular-dispersed fuel-air mixture, and a colloid-dispersedand molecular-dispersed fuel-air mixture; and a hydraulic system with ablockable fuel valve which, during heating and prior to combustion, andduring cooling following combustion, maintains the liquid fuel at apressure increased above ambient pressure and excludes air, and whichkeeps the liquid fuel under pressure during heating, during combustionand during cooling, wherein said blockable fuel valve has a tappet,wherein the closing force of said tappet is greater during the burningstart and switch-off phases than the force created by the differencebetween the forward and return flow pressure, which acts in the opposingdirection of said closing force on said valve tappet.
 2. The burner asdefined in claim 1, wherein said nozzle is a twist nozzle, said twistnozzle being designed as a return flow nozzle with an integrated needlevalve.
 3. The burner as defined in claim 2, wherein said nozzle definesan opening, and wherein said needle valve unblocks said nozzle openingat a defined, adjustable pressure difference between a forward andreturn flow pressure.
 4. The burner as defined in claim 2, furthercomprising: a check valve placed in each fuel line, wherein the linescarrying fuel are closed airtight by means of said needle valveintegrated into said return flow nozzle, and by said check valves. 5.The burner as defined in claim 1, wherein the fuel used is such thatsaid at least one fuel heater generates a preheating temperature whichis set sufficiently high that the fuel can be vaporized underatmospheric conditions.
 6. The burner as defined in claim 1, whereinsaid nozzle defines an outlet, and wherein the heated fuel is almostcompletely vaporized by a pressure reduction at said nozzle outlet andmixed with preheated combustion air of the same temperature.
 7. Theburner as defined in claim 6, wherein part of the fuel forms saidcolloid-dispersed system and the other part of the fuel forms saidmolecular-dispersed system with the supplied combustion air after thepressure reduction at said nozzle outlet and mixing with one of: onlyslightly preheated combustion air and not preheated combustion air. 8.The burner as defined in claim 1, further comprising: means defining apermeable reaction zone for burning the fuel dispersed in the combustionair.
 9. The burner as defined in claim 8, wherein said at least one fuelheater is an electrically operated fuel heater coupled to said reactionzone, wherein the fuel/air mixture is ignited by the surface temperatureof said electrically operated fuel heater.
 10. The burner as defined inclaim 1, further comprising: an air heater; and a return flow nozzlewith an integrated needle valve, wherein said at least one fuel heater,said air heater and said return flow nozzle are provided for preparingthe fuel.
 11. The burner as defined in claim 1, further comprising: afuel regulating device; and burner control means, wherein the pressuredifference between a forward and return flow pressure during a burneroperating cycle is changed by said burner control means according to oneof: continuously, in stages, and pulsating, depending on said fuelregulating device employed.
 12. The burner as defined in claim 1,wherein said colloid-dispersed and/or said molecular-dispersed fuel-airmixture is burned.
 13. The burner as defined in claim 1, furthercomprising: a recirculating pump, wherein said recirculating pumptransfers fuel by pumping during the burner start phase when thepressure difference between the forward and return flow pressure issmall and said blockable fuel valve is closed.
 14. The burner as definedin claim 1, further comprising: a fuel pump; and a heat exchanger,wherein that fuel which is conveyed back to said fuel pump is used forpreheating the combustion air in said heat exchanger.
 15. The burner asdefined in claim 1, further comprising: a fuel feed line; a fuel returnflow line; and a fuel valve connecting the fuel feed line and the fuelreturn flow line, wherein as a result of: one of a defined pressuredifference between the pressure in said feed line and the pressure insaid return flow line; a defined temperature of the fuel in an interiorchamber of said fuel valve; and a defined pressure difference betweenthe pressure in said feed line and the pressure in said return flow lineand the defined temperature of the fuel in said interior chamber of saidfuel valve, said fuel valve is opened.
 16. The burner as defined inclaim 15, wherein said fuel valve comprises a simplex nozzle having aclosing piston.
 17. The burner as defined in claim 15, wherein said fuelvalve is such that when it is open an induction effect is generated forthe combustion air thus making possible the operation of the burnerwithout the need of a blower.
 18. The burner as defined in claim 1,further comprising: a pressure compensation vessel provided in said feedline.
 19. The burner as defined in claim 18, wherein said compensationvessel comprises a bellows.
 20. The burner as defined in claim 19,wherein said bellows is a metal bellows.
 21. A prevaporizing andpremixing burner for liquid fuels, comprising: at least one fuel heaterfor heating the liquid fuel; means for increasing the pressure of theliquid fuel; a nozzle for atomizing and vaporizing the fuel and formixing the fuel with combustion air, wherein at least a portion of thevaporized fuel condenses, creating thereby one of: a colloid-dispersedfuel-air mixture, a molecular-dispersed fuel-air mixture, and acolloid-dispersed and molecular-dispersed fuel-air mixture; a hydraulicsystem with a blockable fuel valve which, during heating and prior tocombustion, and during cooling following combustion, maintains theliquid fuel at a pressure increased above ambient pressure and excludesair, and which keeps the liquid fuel under pressure during heating,during combustion and during cooling; an air heater; a return flownozzle with an integrated needle valve, wherein said at least one fuelheater, said air heater and said return flow nozzle are provided forpreparing the fuel; and a fuel regulating device which opens the bore ofsaid return flow nozzle by means of a needle valve in said return flownozzle by one of: lowering said return flow pressure; raising saidforward flow pressure; and lowering said return flow pressure andraising said forward flow pressure, when the required fuel temperaturehas been reached, such that a mixture formation is made possible.
 22. Aprevaporizing and premixing burner for liquid fuels, comprising: atleast one fuel heater for heating the liquid fuel; means for increasingthe pressure of the liquid fuel; a nozzle for atomizing and vaporizingthe fuel and for mixing the fuel with combustion air, wherein at least aportion of the vaporized fuel condenses, creating thereby one of: acolloid-dispersed fuel-air mixture, a molecular-dispersed fuel-airmixture, and a colloid-dispersed and molecular-dispersed fuel-airmixture; a hydraulic system with a blockable fuel valve which, duringheating and prior to combustion, and during cooling followingcombustion, maintains the liquid fuel at a pressure increased aboveambient pressure and excludes air, and which keeps the liquid fuel underpressure during heating, during combustion and during cooling; meansdefining a permeable reaction zone for burning the fuel dispersed in thecombustion air; and a fuel regulating device, wherein the fuel supply insaid permeable reaction zone is switched off by one of: raising thereturn flow pressure; lowering the forward flow pressure; and raisingthe return flow pressure and lowering the forward flow pressure to thelevel of the return flow pressure, depending on said fuel regulatingdevice used.